FSQ0765RQUDTU Fairchild Semiconductor, FSQ0765RQUDTU Datasheet - Page 12

• Manufacturer Part Number: FSQ0765RQUDTU
• Description: IC CONV QUASI-RES 650V TO-220F-6
• Manufacturer: Fairchild Semiconductor
• Series: FPS™r

Specifications of FSQ0765RQUDTU

• Output Isolation: Isolated
• Frequency Range: 48kHz ~ 67kHz
• Voltage - Input: 9 V ~ 20 V
• Voltage - Output: 650V
• Power (watts): 90W
• Operating Temperature: -25°C ~ 85°C
• Package / Case: TO-220-6 Formed Leads
• On Resistance (max): 1.3 Ohms
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: + 25 C
• Maximum Power Dissipation: 45 W
• Mounting Style: Through Hole
• Off Time (max): 63 ns
• On Time (max): 27 ns
• Operating Frequency: 66.7 KHz
• Propagation Delay Time: 200 ns
• Supply Current: 3 mA
• Supply Voltage (max): 20 V
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

FSQ0765RQ Rev. 1.0.1
© 2008 Fairchild Semiconductor Corporation
Functional Description
1. Startup: At startup, an internal high-voltage current
source supplies the internal bias and charges the
external capacitor (C
illustrated in Figure 22. When V
FPS™ begins switching and the internal high-voltage
current source is disabled. The FPS continues its normal
switching operation and the power is supplied from the
auxiliary transformer winding unless V
stop voltage of 8V.
2. Feedback Control: FPS employs current-mode
control, as shown in Figure 23. An opto-coupler (such as
the FOD817A) and shunt regulator (such as the KA431)
are typically used to implement the feedback network.
Comparing the feedback voltage with the voltage across
the R
switching duty cycle. When the reference pin voltage of
the shunt regulator exceeds the internal reference
voltage of 2.5V, the opto-coupler LED current increases,
pulling down the feedback voltage and reducing the duty
cycle. This typically happens when the input voltage is
increased or the output load is decreased.
2.1 Pulse-by-Pulse Current Limit: Because current-
mode control is employed, the peak current through the
SenseFET is limited by the inverting input of PWM
comparator (V
that the 0.9mA current source flows only through the
internal resistor (3R + R = 2.8k), the cathode voltage of
diode D2 is about 2.5V. Since D1 is blocked when the
feedback voltage (V
voltage of the cathode of D2 is clamped at this voltage,
clamping V
through the SenseFET is limited.
FSQ0765R Rev.00
sense
8V/12V
FB
resistor makes it possible to control the
*. Therefore, the peak value of the current
Figure 22. Startup Circuit
FB
3
*), as shown in Figure 23. Assuming
V
CC
FB
a
) connected to the V
) exceeds 2.5V, the maximum
C
a
V
CC
good
CC
CC
reaches 12V, the
I
CH
goes below the
Internal
Bias
V
V
CC
ref
6
DC
V
pin, as
str
12
2.2 Leading-Edge Blanking (LEB): At the instant the
internal SenseFET is turned on, a high-current spike
usually occurs through the SenseFET, caused by
primary-side capacitance and secondary-side rectifier
reverse recovery. Excessive voltage across the R
resistor would lead to incorrect feedback operation in the
current-mode PWM control. To counter this effect, the
FPS employs a leading-edge blanking (LEB) circuit. This
circuit inhibits the PWM comparator for a short time
(t
3. Synchronization: The FSQ-series employs a quasi-
resonant switching technique to minimize the switching
noise and loss. The basic waveforms of the quasi-
resonant converter are shown in Figure 24. To minimize
the MOSFET's switching loss, the MOSFET should be
turned on when the drain voltage reaches its minimum
value, which is indirectly detected by monitoring the V
winding voltage, as shown in Figure 24.
V
FSQ0765R Rev. 00
LEB
O
Figure 24. Quasi-Resonant Switching Waveforms
Figure 23. Pulse-Width-Modulation (PWM) Circuit
V
) after the SenseFET is turned on.
V
MOSFET Gate
sync
ds
ON
FOD817A
KA431
V
FB
V
1.2V
DC
C
B
4
I
delay
V
V
SD
CC
t
F
D1
V
ref
230ns Delay
V
I
FB
D2
+
FB
V
-
V
1.0V
RO
*
RO
V
ovp
3R
ON
R
(8V)
OSC
FSQ0765R Rev.00
OLP
www.fairchildsemi.com
driver
Gate
R
SenseFET
sense
sense
CC